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Hey all, I'm new to the whole world of forced-induction, and as I am running a 4G63T in my Locost, I should probably get to learning. I know the basics of how they work, but what I am more unsure about is modifications, and what is actually helpful. So I'm gonna start off asking about two things: External waste gates and blow-off valves.

I am running a stock motor and stock (maybe ported) 14b turbo, and mild tuning software with a wide-band and a manual boost controller.

I got a real Greddy blow-off valve thrown in with a deal when I bought my wiring harness and the boost controller. What purpose does a good BOV have besides the noise?

Also, is it worth it to invest in an external waste gate? The 14b has one built in that is supposed to be pretty good but I don't really know how an external one helps.

Thanks as always for the help!

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is

Blow off valves and waste gates do two different things. ..
A waste gate sets the upper limit for boost while under throttle, it allows exhaust to bypass the exhaust turbine when the intake manifold pressure is at the desired limit.
A blow off valve is used when the intake turbine is ahead of the throttle plate, it functions to (hopefully) eliminate a reverse pressure wave resulting from the throttle plate closing (like when you lift to shift) that would cause the turbine to slow down and induce "turbo lag".
Two different relief valves, two different functions. ..

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

I don't know that there is much point in an external wastegate if the internal one doesn't have any problems keeping the boost level totally under control.

I also prefer the quieter and more efficient operation of a recirculated blow off valve (diverter valve) that returns the excess pressure in the intake tract back to the inlet side of the turbo, over the ever popular vent to atmosphere blow off valves.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

You're asking questions about a very involved field. I highly recommend reading to bring yourself up to speed and Garrett's website is great. I also recommend the book "Street Turbocharging."

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Thunder, I tell people to read this 10 times and then ask questions. It's Miata specific but it covers all the aspects of turbo changing.

http://www.miataturbo.net/diy-turbo-dis ... post-4288/

Graham

FastG, I'll have to read up on that soon. I also found out my Dad has a copy of the Corky Bell book "Maximum Boost." I'll be reading that in my spare time as well. At this point I think I am going to pass on the external wastegate, but I may use my BOV since I already have one.

If anyone else wants to pitch in, that would be great, otherwise thank you to the guys that did already!

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is

Thunder, unless your building a "turbo" engine, you can pass on a external waist gate. It's only when you get up into the high boost number that can become necessary. But if your running a regular motor it's not a requirement.

Graham

Graham-

I'm not understanding what you mean. Do you mean like am I building a serious turbo motor or just any motor with a turbo? Cause I am using a turbocharged engine but it comes turbocharged from the factory.

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is

I did not realize you were starting with a turbo motor, but it changes little. How much boost are you planning on using compared to stock? If your using double the stock boost you will have to build a serious turbo motor. If your playing at or around stock boost you should be fine. I stock Miata will take about 14psi boost if your engine management is good. But over 14 pounds you will need to start building a special engine.

Graham

Looks like stock those motors run 8-12 pounds of boost. I may squeeze a couple more pounds out of it but it really comes down to how good I am at tuning, as well as how well my intake and exhaust will flow.

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is

Intake and exhaust flow when turbocharging. ...
I remember replacing a rotted out exhaust on a turbo Subie I had. ... it was as if I had added 10 lbs to the flywheel.
Increased back pressure on the hot side made it spin up slower and, I think, limited the gross power output.
It didn't affect the top boost pressure but it sure made it take longer to get there. ..

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

You won't (shouldn't) NEED an external wastegate til much higher boost levels. Anything under 15psi should be fine.
You don't need a blow off valve either. Nor do you need a bypass valve (recirculated rather than vented). If you like the noise, go for it. Blocking off the bov-adapter on my turbo car was top 3 mods I've done to it. Initial turbo lag didn't change (still on stock turbo, so it spools just fine) but there was no loss of boost pressure between shifts, so it starts to accelerate as soon as you get on the gas, rather than waiting a bit for the turbo to respool.
Not to mention the flutter puts a smile on my face every time I hear it.

Jeimuzu

That sounds like a recipe for some major compressor surge which I KNOW is not a good thing. The only car I knew of that didn't run a BOV was my Dad's E36 M3 because he used an Aerodyne variable-vane turbo which could compensate at the 7-8 psi he was running.

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is

It's not a good thing, but compressor surge during shifts isn't end-of-the-world bad either. It's compressor surge under load that will grenade your turbo.

Fair enough, I'm going to run the BOV because I already have one, and it gives me a little extra flash under the hood, but I will pass on the external wastegate.

_________________
--Eric

"Stuckness shouldn't be avoided. It's the psychic predecessor of all real understanding." --Robert Pirsig

Grey 2019 Hyundai Veloster Turbo
Red 1989 BMW 325is